1. Field of the Invention
The present invention relates to a thermal diffusion sheet that diffuses heat from a thermally conductive component of a semiconductor component such as a light emitting diode (LED) and a heat generating portion of an image display apparatus such a plasma display (PDP) or a liquid crystal display (LCD), and a method for mounting the thermal diffusion sheet.
2. Description of Related Art
A semiconductor such as a computer (CPU), a transistor, or a light emitting diode (LED), a power module, a plasma display (PDP), a liquid crystal display (LCD), etc. generate heat during operation and the performance can decrease due to the heat. For this reason, electronic components that generate heat are provided with a heat dissipating element. A graphite sheet is known to have an excellent thermal conductivity in the plane direction, and thus has been used as a heat dissipating material by utilizing its thermal conductivity. The graphite sheet itself is brittle and cannot be handled easily. Therefore, the graphite sheet is reinforced with a film, which also imparts electrical insulation properties to the graphite sheet. When such a graphite sheet is mounted actually, it needs to be fixed temporarily to a heat generating element or a heat dissipating element. For this purpose, Patent Document 1 proposes the use of a double-sided tape or an adhesive layer that is formed by applying an adhesive directly to the graphite sheet. Patent Documents 2, 3 propose examples in which the graphite sheet is used for the light emitting diode or the liquid crystal display (LCD).
In the case of a semiconductor mounted on an electric circuit, because of the electrical conductivity as well as the brittleness of the graphite sheet, graphite powder may come off the graphite sheet, fall on the electric circuit, and cause a short circuit. To solve this problem, Patent Document 4 proposes that a graphite sheet, supporting films disposed on both sides of the graphite sheet, and spacers attached to the end faces of the graphite sheet are formed integrally together.
However, in Patent Document 4, since the adhesive layer itself has thermal insulation properties, a further improvement in heat conduction is required. In many cases, a general double-sided tape includes a thin film as a core and adhesive layers formed on both sides of the thin film. Although the thin film serves to reinforce the graphite sheet, if the thin film is not present as a core, the graphite sheet absorbs the substances constituting the adhesive layer. Thus, the adhesive strength is reduced due to aging deterioration. In particular, when an adhesive layer is formed directly on the graphite sheet, the phenomenon of reducing the adhesive strength due to aging deterioration is prominent. Moreover, the double-sided tape and the adhesive are likely to have a low thermal conductivity. Therefore, even if the graphite sheet has a high thermal conductivity in the plane direction, such a low thermal conductivity of the material, in which heat is transferred before reaching the graphite sheet, is not desirable for the efficiency of “heat transfer”.
In the conventional technology, the double-sided tape, the adhesive, and the insulating film are likely to have a low thermal conductivity, and even if the graphite sheet with a high thermal conductivity in the plane direction is used, such a low thermal conductivity of the material, in which heat is transferred before reaching the graphite sheet, is a problem in the efficiency of “heat transfer”.
Patent Document 1: JP 11(1999)-317480 A
Patent Document 2: JP 2007-108547 A
Patent Document 3: JP 2008-028352 A
Patent Document 4: JP 2007-044994 A